Surface charge density variation to promote structural orientation of cellulose nanocrystals

Cellulose nanocrystals (CNC) were prepared at three different surface charge densities. Their aggregation pattern in water, with and without ionic strength, was conducted in dilute conditions (0.1 g/l). Morphologies of the resulting self-assembled structures were investigated by atomic force microscopy (AFM). In conditions devoid of ionic strength, we demonstrate that neutral CNC can self-assemble, following a slow aggregation process, to form elongated fibrilar structures of several microns while the thickness keeps around 29 nm. In the same conditions, sulfated CNC remained as individual objects. When ionic strength was increased to 50 mM NaCl, charged CNC aggregated slightly compared to the neutral CNC but NaCl promoted larger aggregates due to a faster process. This study reveals a new self-aggregation process of neutral CNC, leading to CNC particles with fibrilar morphology revealing an aspect ratio that can be over 60.